This invention relates to a tuner module for a radio receiver and, in particular, relates to a tuner module suitable for an automobile digital radio receiver capable of listening to digital radio broadcasting by receiving radiowaves from an artificial satellite (hereinafter referred to as “satellite waves”) or radiowaves on the ground (hereinafter referred to as “ground waves”).
Recently, digital radio receivers capable of listening to digital radio broadcasting by receiving satellite waves or ground waves have been developed and put to practical use in the U.S. The digital radio receiver is generally mounted in a mobile body such as an automobile and is capable of listening to radio broadcasting by receiving radiowaves with frequencies in about 2.3 GHz band. That is, the digital radio receiver is a radio receiver capable of listening to mobile broadcasting. Since the frequency of the received radiowave is in about 2.3 GHz band, the received wavelength (resonant wavelength) λ is about 128.3 mm. The ground wave is a radiowave obtained by once receiving a satellite wave at an earth station, slightly shifting it in frequency, and then retransmitting it as a linearly polarized wave. That is, the satellite wave is a circularly polarized wave, while the ground wave is a linearly polarized wave.
As digital radio receivers, there are not only the type adapted to be mounted in an automobile, but also a type adapted to be installed in a house or the like, and further a type that is portable using a battery as a power source.
In any case, since the radiowaves having the frequencies in about 2.3 GHz band are used in the digital radio broadcasting, received signals are input into a tuner through an antenna device receiving the radiowaves. Normally, components constituting the tuner are mounted on a printed wiring board and placed in a metal case also serving as a shield (see, e.g. Japanese Unexamined Patent Application Publication (JP-A) No. H06-209268).
The structure of a satellite digital radio receiver will be explained as one example with reference to FIG. 1. In FIG. 1, the satellite digital radio receiver comprises an antenna 101, a tuner section 102, a signal demodulation section 103, a channel demodulation section 104, a sound decoder 105, a data decoder 106, a control section 107, and an operating section 108 (see, e.g. Japanese Unexamined Patent Application Publication (JP-A) No. 2002-344335).
In the meantime, the components constituting the tuner include IC components. The IC components of this type often require means for radiating heat generated therefrom. This is because if the heat radiation from the IC components is insufficient so that the IC components are raised to a high temperature, it may cause deterioration in reception state. A heatsink is often used as the heat radiating means for the IC components. The heatsink is often a combination of structures having cooling fins, which, however, increases in overall size and thus is not suitable particularly for the case where miniaturization is required.